Vehicle steering telescopic shaft

ABSTRACT

A vehicle steering telescopic shaft having a male shaft and a female shaft so fitted to each other as not to be rotatable but to be slidable. First torque transmitting members are disposed between the male shaft and the female shaft, and roll when the male shaft and the female shaft make relative movements in axial directions. Elastic members are disposed adjacent in a radial direction to the first torque transmitting members and restrict them when rotated and apply a pre-load to the male shaft and the female shaft through the first torque transmitting members when not rotated. Second torque transmitting members are provided between the male shaft and the female shaft, and slide when the male shaft and the female shaft make the relative movements in the axial directions, and transmit a torque when rotated.

TECHNICAL FIELD

The present invention relates to a telescopic shaft for a vehiclesteering.

BACKGROUND ARTS

A steering mechanism unit of an automobile has hitherto involved the useof, as a part of the steering mechanism unit, a telescopic shaftabsorbing an axial displacement occurred when the automobile travels andincluding a male shaft and a female shaft that are spline-fitted to eachother in order not to transfer the displacement and vibrations onto asteering wheel. What is required of the telescopic shaft is to reducebacklash noises at the spline portion, to reduce a feeling of backlashon the steering wheel and to reduce a slide resistance when sliding inaxial directions.

For these requirements, the spline portion of the male shaft of thetelescopic shaft is coated with a nylon layer, and further a grease isapplied over a sliding portion, thereby absorbing or relieving metalnoises, metal butting sounds, etc. and also reducing the slideresistance and the backlash in a rotating direction. In this case, aprocessing flow of forming the nylon layer is: cleaning theshaft→coating a primer→heating→coating nylon powder→roughcutting→finish-cutting→selective fitting to the female shaft. A finalcutting work is conducted in a way that selects dies adjusted to anaccuracy of the already-worked female shaft.

It is required that even the backlash be restrained to the minimum whilerestraining a slide load on the telescopic shaft to the minimum, andhence the final cutting work has no option but to select the diesmatched with the female shaft which differ by every several microns insize of an over-pin diameter and to perform working, with the resultthat a rise in working cost is brought about. Moreover, the backlash inthe rotating direction increases as an abrasion of the nylon layerprogresses with transitions of the use.

Further, under such a condition as to be exposed to a high temperaturein an engine room, the nylon layer changes in volume as followed by aremarkable rise in slide resistance and a remarkably-acceleratedprogression of the abrasion, and therefore the backlash in the rotatingdirection increases.

Accordingly, there is a demand for providing the telescopic shaftemployed for the steering shaft for the automobile with a simple andlow-cost structure capable of restraining over a long period of time anemission of heterogeneous sounds due to the backlash in the rotatingdirection and deterioration in the feeling of steering.

DISCLOSURE OF THE INVENTION

It is an object of the present invention, which was devised under suchcircumstances described above, to provide a telescopic shaft for avehicle steering that is capable of actualizing a stable slide load,surely preventing a backlash in a rotating direction and transferring atorque in a high-rigidity state.

To accomplish the above object, the present invention provides atelescopic shaft for a vehicle steering, assembled into a steering shaftof a vehicle and having a male shaft and a female shaft that are sofitted to each other as not to be rotatable but to be slidable, beingcharacterized by comprising: a first torque transmitting deviceconstructed of a first interposing portion provided in an outerperipheral surface of the male shaft and in an inner peripheral surfaceof the female shaft, first torque transmitting members disposed in thefirst interposing portion and rolling when the male shaft and the femaleshaft make relative movements in axial directions, and elastic membersdisposed respectively adjacent in a radial direction to the first torquetransmitting members in the first interposing portion, restricting thefirst torque transmitting members when rotated and applying a pre-loadto the male shaft and the female shaft through the first torquetransmitting members when not rotated; and a second torque transmittingdevice constructed of a second interposing portion provided in the outerperipheral surface of the male shaft and in the inner peripheral surfaceof the female shaft, and second torque transmitting members disposed inthe second interposing portion, sliding when the male shaft and thefemale shaft make the relative movements in the axial directions, andtransmitting a torque when rotated.

Further, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the first interposingportion and the second interposing portion be structured of first axialgrooves and second axial grooves that are formed in pairs respectivelyin an outer peripheral surface of the male shaft and an inner peripheralsurface of the female shaft.

Still further, in the telescopic shaft for the vehicle steeringaccording to the present invention, it is preferably that the firsttorque transmitting device and the second torque transmitting device bedisposed in positions different in a peripheral direction between themale shaft and the female shaft.

Yet further, in the telescopic shaft for the vehicle steering accordingto the present invention, it is preferable that the first interposingportion of the first torque transmitting device be structured of thefirst axial groove and the second axial groove that are formed in themale shaft and in the female shaft, and the first torque transmittingmembers consist of a plurality of spherical members disposed in thefirst axial groove and in the second axial groove, the secondinterposing portion of the second torque transmitting device bestructured of two sets of third axial grooves and fourth axial groovesthat are disposed apart from each other in a circumferential direction,and the second torque transfer members consist of cylindrical membersdisposed in the third and fourth axial grooves, of which axialdirections are set parallel with the male shaft and with the femaleshaft.

Moreover, in the telescopic shaft for the vehicle steering according tothe present invention, the first interposing portion be structured ofplural pairs of axial grooves formed between the male shaft and thefemale shaft, and the second interposing portion be structured of pluralpairs of axial grooves disposed between the adjacent pairs of axialgrooves of the first interposing portion.

As described above, the telescopic shaft for the vehicle steeringincludes: the first torque transmitting device constructed of the firstinterposing portion provided in the outer peripheral surface of the maleshaft and in the inner peripheral surface of the female shaft, the firsttorque transmitting members disposed in the first interposing portionand rolling when the male shaft and the female shaft make the relativemovements in the axial directions, and the elastic members disposedadjacent in the radial direction to the respective first torquetransmitting member in the first interposing portion, restricting thefirst torque transmitting members when rotated and applying the pre-loadto the male shaft and the female shaft through the first torquetransmitting members when not rotated; and the second torque transferdevice constructed of the second interposing portion provided in theouter peripheral surface of the male shaft and in the inner peripheralsurface of the female shaft, and the second torque transmitting membersdisposed in the second interposing portion, sliding when the male shaftand the female shaft make the relative movements in the axialdirections, and transmitting a torque when rotated. Then, the firstinterposing portion and the second interposing portion are structured ofthe first axial grooves and the second axial grooves that are formed inpairs respectively in the outer peripheral surface of the male shaft andthe inner peripheral surface of the female shaft.

When the torque is not transmitted, the telescopic shaft for the vehiclesteering according to the present application is, with the first torquetransmitting device and the second torque transmitting device employed,the elastic members applying the pre-load to the first torquetransmitting members and to the second torque transmitting membersagainst the female shaft to such an extent as to not cause a backlash,capable of surely preventing the backlash between the male shaft and thefemale shaft and making the male shaft and the female shaft slide in theaxial directions with the stable slide load without any backlash.

On the other hand, when the torque is transmitted, the telescopic shaftfor the vehicle steering according to the present application is, theelastic member being able to restrict the first transmitting members andthe second torque transmitting members in the peripheral direction,capable of surely preventing the backlash in the rotating directionbetween the male shaft and the female shaft and transferring the torquein the high-rigidity state.

Further, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the first torquetransmitting members consist of cylindrical members disposed so that anaxial direction thereof is set in a direction intersecting the maleshaft and the female shaft.

Moreover, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the elastic members becomposed of plate springs.

Furthermore, in the telescopic shaft for the vehicle steering accordingto the present invention, it is preferable that the axial grooveincludes a shallow portion and a deep portion, the shallow portion ofthe groove be formed in a curved-surface shape, while the deep portionof the groove be formed in a flat shape, the first torque transmittingmember and the second torque transmitting member abut on each other inthe vicinity of a boundary point between the curved-surface portion andthe flat portion.

Further, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the male shaft be providedwith a groove end portion for generating a large slide by restrictingthe first torque transmitting members form rolling in the axialdirections when a collision happens, and for supplementally absorbing animpact energy when the collision happens.

Still further, in the telescopic shaft for the vehicle steeringaccording to the present invention, it is preferable that a gap betweenthe male shaft, the second torque transmitting member and the femaleshaft be arbitrarily set by properly selecting a diameter of the secondtorque transmitting member or combining diameters thereof.

Yet further, in the telescopic shaft for the vehicle steering accordingto the present invention it is preferable that the elastic members arein contact with the respective first torque transmitting members at acertain fixed contact angle, generate pre-load in the radial directionand in the peripheral direction when a torque is not inputted to themale shaft or the female shaft, and generate the pre-load in theperipheral direction when the torque is inputted to the male shaft orthe female shaft.

Moreover, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the first torquetransmitting devices be disposed in the three pairs of axial groovesarranged equally at an interval of 120 degrees in the peripheraldirection, and the second torque transmitting devices be disposedbetween the three pairs of axial grooves.

Furthermore, in the telescopic shaft for the vehicle steering accordingto the present invention, it is preferable that the second torquetransmitting devices be disposed respectively in central portions in theperipheral direction between the three pairs of axial grooves.

Still furthermore, in the telescopic shaft for the vehicle steeringaccording to the present invention, it is preferable that a first torquetransmitting member holder for holding the first torque transmittingmembers in a rollable manner be disposed in a telescopic shaft for avehicle steering in which the fist torque transmitting device and thesecond torque transmitting device are disposed between the male shaftand the female shaft.

Yet furthermore, in the telescopic shaft for the vehicle steeringaccording to the present invention, it is preferable that the holder haselongate holes or a plurality of round holes arranged extending in theaxial directions of the male shaft and of the female shaft, and thefirst torque transmitting members be disposed in the elongate holes orin the plurality of round holes.

Further, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the holder takes acylindrical shape and has elongate holes or a plurality of round holesarranged extending in the axial directions of the male shaft and of thefemale shaft, and the first torque transfer members be disposed in theelongate holes or in the plurality of round holes.

Moreover, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the holder taking thecylindrical shape has interference avoiding elongate holes for avoidinginterference with the second torque transmitting device or aninterference avoiding open slit opened at its side end portion.

Further, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that a total length of theinterference avoiding elongate holes or the open slits for avoiding theinterference with the second torque transmitting device, be longer thana total length of the elongate holes or a train of the plurality ofround holes for holding the first toque transmitting members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of a telescopic shift for a vehicle steering in afirst embodiment of the present invention;

FIG. 1B is a perspective view thereof;

FIG. 2 is a cross sectional view taken along the line A-A in FIG. 1A;

FIG. 3 is a perspective view of a state where a male shaft and a femaleshaft of the telescopic shaft shown in FIG. 1 are separated;

FIGS. 4A and 4B are plan views each showing an example of a platespring;

FIG. 4C is a exploded perspective view of the telescopic shaft shown inFIG. 1;

FIG. 5 is a graph showing a relationship between a stroke and a slideload of the telescopic shaft for the vehicle steering in the firstembodiment;

FIG. 6 is a cross sectional view of the telescopic shaft for the vehiclesteering in a second embodiment of the present invention;

FIG. 7 is an exploded perspective view of the telescopic shaft for thevehicle steering in a third embodiment of the present invention;

FIG. 8 is a perspective view of a holder shown in FIG. 7;

FIG. 9 is a cross sectional view of the telescopic shaft for the vehiclesteering in the first embodiment of the present invention;

FIG. 10 is a cross sectional view of the telescopic shaft for thevehicle steering in a fourth embodiment of the present invention;

FIG. 11 is a perspective view of the holder shown in FIG. 10;

FIG. 12 is vertical sectional view of the telescopic shaft for thevehicle steering with a Cardan shaft joint in a first example of a fifthembodiment of the present invention;

FIGS. 13A through 13E are views each showing an instance of the femaleshaft in the first example of the fifth embodiment;

FIG. 14 is a view showing an instance of the female shaft in the firstexample of the fifth embodiment;

FIGS. 15A through 15E are views each showing an instance of the maleshaft in first and second examples of the fifth embodiment;

FIG. 16 is a vertical sectional view of the telescopic shaft for thevehicle steering in THE second example of the fifth embodiment of thepresent invention;

FIG. 17 is a vertical sectional view of the female shaft illustrated inFIG. 16;

FIG. 18 is a cross sectional view of a principal portion of thetelescopic shaft for the vehicle steering in the prior art;

FIG. 19 is a cross sectional view of a principal portion of thetelescopic shaft for the vehicle steering in a sixth embodiment of thepresent invention;

FIGS. 20A and 20B are respectively vertical sectional views of thetelescopic shaft for the vehicle steering in a seventh embodiment of thepresent invention, showing a collapsible state when a secondarycollision of the vehicle happens;

FIGS. 21A and 21B are vertical sectional views of the telescopic shaftfor the vehicle steering illustrated in FIG. 19, showing the collapsiblestate when the secondary collision of the vehicle happens;

FIGS. 22A through 22D are graphs each showing a relationship between thestroke and the slide load of the telescopic shaft for the vehiclesteering shown in FIGS. 20 and 21;

FIG. 23A is a vertical sectional view of the telescopic shaft for thevehicle steering in an eighth embodiment of the present invention;

FIG. 23B is a cross sectional view taken along the line b-b in FIG. 23A;

FIG. 24 is an exploded perspective view of the telescopic shaft for thevehicle steering in the eighth embodiment;

FIG. 25 is a graph (a characteristic line graph obtained when fixing oneside end of the male or female shaft and inputting a torque from theother side end) showing a relationship between a rotational angle andthe torque of the telescopic shaft;

FIG. 26 is a graph showing a relationship between the rotational angleand the torque of the telescopic shaft;

FIG. 27 is a cross sectional view of a principal portion of thetelescopic shaft for the vehicle steering in the prior art;

FIG. 28 is a cross sectional view of a principal portion of thetelescopic shaft for the vehicle steering in a ninth embodiment of thepresent invention;

FIG. 29 is a cross sectional view of the principal portion of thetelescopic shaft for the vehicle steering illustrated in FIG. 28,showing an operation thereof;

FIG. 30A is a graph showing a relationship between the rotational angleand the torque of the telescopic shaft in the prior art;

FIG. 30B is a graph showing a relationship between the rotational angleand the torque of the telescopic shaft in the ninth embodiment;

FIG. 31A is a vertical sectional view of the telescopic shaft for thevehicle steering in a tenth embodiment of the present invention;

FIG. 31B is a cross sectional view taken along the line b-b in FIG. 31A;

FIG. 32 is a graph showing a relationship between a stroke and a slideload in the tenth embodiment;

FIG. 33A is a vertical sectional view of the telescopic shaft for thevehicle steering in an eleventh embodiment of the present invention;

FIG. 33B is a cross sectional view taken along the line b-b in FIG. 33A;

FIG. 34A is a perspective view of a holder shown in FIG. 33;

FIGS. 34B and 34C are respectively perspective views of the holder inexamples of the eleventh embodiment;

FIGS. 35A, 35B and 35C are respectively perspective views of the holderin examples of the eleventh embodiment; and

FIG. 36 is a side view of a steering mechanism unit of an automobile, towhich the telescopic shaft for the vehicle steering in the embodiment ofthe present invention is applied.

EMBODIMENTS OF THE INVENTION

A telescopic shaft for a vehicle steering in an embodiment of thepresent invention will be described with reference to the drawings.

FIG. 36 is a side view of a steering mechanism unit of an automobile, towhich the telescopic shaft for the vehicle steering in the embodiment ofthe present invention is applied.

Referring to FIG. 36, the steering mechanism unit is constructed of anupper steering shaft member 120 (including a steering column 103 and asteering shaft 104 rotatably held in the steering column 103) attachedto a car-body-sided member 100 through an upper bracket 101 and a lowerbracket 102, a steering wheel 105 secured to an upper end of thesteering shaft 104, a lower steering shaft member 107 connected via auniversal joint 106 to a lower end of the steering shaft 104, a pinionshaft 109 connected via a steering shaft joint 108 to the lower steeringshaft member 107, a steering rack shaft 112 connected to the pinionshaft 109, and a steering rack support member 113 that supports thissteering rack shaft 112 and is fixed through an elastic member 111 to adifferent frame 110 on the car body.

Herein, the upper steering shaft member 120 and the lower steering shaftmember 107 utilize the telescopic shaft for the vehicle steering (whichwill hereinafter be simply called the telescopic shaft) in accordancewith the embodiment of the present invention. The lower steering shaftmember 107 is constructed by fitting a male shaft into a female shaft.What is required of this type of lower steering shaft member 107 is,however, a performance of absorbing an axial displacement occurred whenthe automobile travels and preventing this displacement and vibrationsfrom being transmitted onto the steering wheel 105. Such a performanceis required in the case of a structure where the car body is of asub-frame structure, the member 100 for fixing the upper portion of thesteering mechanism is separate from the frame 110 to which the steeringrack support member 113 is fixed, and the steering rack support member113 is fastened and fixed to the frame 110 through the elastic member111 such as a rubber. Further, there is other case in which aretractable function is needed because of a worker's fitting andfastening the telescopic shaft, after temporarily shrinking it, to thepinion shaft 109 on the occasion of fastening the steering shaft joint108 to the pinion shaft 109. Moreover, the upper steering shaft member120 provided in a comparatively upper position of the steering mechanismis also constructed by fitting a male shaft into a female shaft. Thistype of upper steering shaft member 120 is, however, required to have afunction of adjusting a position of the steering wheel 105 by movingthis position in the axial direction in order for a driver to obtain aposition optimal to drive the automobile, and is therefore required tohave an axially retractable function. In all the cases described above,what is required of the telescopic shaft is to reduce the backlashnoises at the fitting portion, to reduce the feeling of backlash on thesteering wheel 105 and to reduce the slide resistance when sliding inthe axial direction.

First Embodiment

FIG. 1A is a side view of the telescopic shaft for the vehicle steeringin a first embodiment of the present invention. FIG. 1B is a perspectiveview thereof. FIG. 2 is a cross sectional view taken along the line A-Ain FIG. 1A. FIG. 3 is a perspective view showing a state where a maleshaft and a female shaft of a telescopic shaft shown in FIG. 1 areseparated. FIGS. 4A and 4B are plan views each showing an example of aplate spring. FIG. 4C is an exploded perspective view of the telescopicshaft for the vehicle steering. FIG. 5 is a graph showing a relationshipbetween a stroke of and a slide load of the telescopic shaft for thevehicle steering in the first embodiment.

As shown in FIG. 1, the telescopic shaft for the vehicle steering (whichwill hereinafter be simply called the telescopic shaft) is constructedof a male shaft 1 and a female shaft 2 that are so fitted as not to berotatable but to be slidable on each other.

As shown in FIG. 2, three lines of axial grooves 3, 4, 4 takingsubstantially a circular-arced shape and disposed at an interval of 120degrees in a peripheral direction, are formed extending on an outerperipheral surface of the male shaft 1. Corresponding thereto, threelines of axial grooves 5, 6, 6 taking substantially the circular-arcedshape disposed at the interval of 120 degrees in the peripheraldirection, are formed extending on an inner peripheral surface of thefemale shaft 2. The axial grooves 3, 5 form a first interposing portion,and the axial grooves 4, 6; 4, 6 form a second interposing portion.

A plate spring 9, which will be explained later on, is provided as apre-loading elastic member formed in substantially an M-shape betweenthe axial groove 3, taking substantially the circular-arced shape insection, of the male shaft 1 and the axial groove 5, takingsubstantially the circular-arced shape, of the female shaft 2; and aplurality of rigid spherical members 7 as first torque transmittingmembers are so interposed as to be rollable between a central concaveportion of the plate spring 9 and the axial groove 5, therebystructuring a first torque transmitting device. Thus, the sphericalmembers 7 roll when the male shaft 1 and the female shaft 2 make theirrelatives movements in the axial direction and are, when rotating,restrained by the plate spring 9 to transmit a torque.

Cylindrical members 8 serving as second torque transmitting members thatpermit the male shaft 1 and the female shaft 2 to make their relativemovements in the axial direction and transmit the torque when rotating,are slidably interposed between two lines of axial grooves 4, 4, eachtaking substantially the circular-arced shape or a Gothic arched shape,of the male shaft 1 and two lines of axial grooves 6, 6, each takingsubstantially the circular-arced shape or the gothic arched shape, ofthe female shaft 2, thereby structuring a second torque transmittingdevice.

Grooves 3 b, 3 b are formed extending in parallel with the groove 3 inthe axial direction on both sides of the axial groove 3 of the maleshaft 1, and stepped portions 3 a, 3 a are formed between the axialgroove 3 and the grooves 3 b, 3 b. Both side ends of the plate spring 9taking substantially the M-shape in section extend respectively down tobottoms of the grooves 3 b, 3 b, and the most end portions are incontact with on the stepped portions 3 a, 3 a so as to pinch thesestepped portions 3 a, 3 a, respectively. Thus, the plate spring 9 islatched at concave portions 9 c, 9 c thereof by the stepped portions 3a, 3 a provided on both sides of the axial groove 3 of the male shaft 1,whereby the whole of the plate spring 9 is unable to move in theperipheral direction when transmitting the torque.

The plate spring 9, when the torque is not transmitted, applies apre-load onto each of the spherical members 7 and the cylindricalmembers 8, 8 to such an extent as not to cause any backlash with respectto the female shaft 2, and, when transmitting the torque, elasticallydeforms to operate for restraining the spherical members 7 in theperipheral direction between the male shaft 1 and the female shaft 2.

Note that two lines of peripheral grooves 10 are, as shown in FIG. 4C,formed in positions of the male shaft 1 in which the two pieces ofcylindrical members 8 and the two side ends of the plate spring 9 aredisposed. Further, as shown in FIG. 4A, protrusions 9 a are formed atboth ends of the plate spring 9 in the axial direction. As shown in FIG.3, two pieces of stop rings 11 are fitted into the two peripheralgrooves 10, thereby fixing the two pieces of cylindrical members 8 inthe axial direction and also having the protrusions 9 a of the platespring 9 firmly engaged with inner peripheries of the stop rings 11. Theprotrusions formed at the both ends of the plate spring 9 in the axialdirection, each may take a configuration as indicated by a symbol 9 b inFIG. 4B.

The plurality of spherical members 7 are held by a holder 12, and thespherical members 7 and the holder 12 are regulated in their axialmovements by the stop rings 11 when sliding.

In the thus structured telescopic shaft, the spherical members 7 and thecylindrical members 8 are interposed between the male shaft 1 and thefemale shaft 2, and the plate spring 9 applies the pre-load onto thespherical members and the cylindrical members 8 to such an extent as notto cause the backlash with respect to the female shaft 2, thereby makingit possible to surely prevent the backlash between the male shaft 1 andthe female shaft 2 and enabling the male shaft 1 and the female shaft 2to slide with a stable slide load without the backlash when making therelative movements in the axial direction.

Note that if the slide surface would be a purely slidable surface as bythe prior arts, there could be nothing but to restrict the pre-loadingfor preventing the backlash to a certain level of load. This is becausethe slide load is what a friction coefficient is multiplied by thepre-load, and, if the pre-load is increased in the hope of preventingthe backlash and improving the rigidity of the telescopic shaft, itfollowed that the situation falls into such a vicious circle that theslide load rises.

In this respect, the first embodiment adopts partially the rollingmechanism, and hence the pre-load could be increased without bringingabout a remarkable increase in the slide load. This enabled attainmentsof preventing the backlash and improving the rigidity, which could notbe accomplished by the prior arts.

According to the first embodiment, when transmitting the torque, theplate spring 9 elastically deforms to restrain the spherical members 7in the peripheral direction between the male shaft 1 and the femaleshaft 2, and besides the two lines of cylindrical members 8 interposedbetween the male shaft 1 and the female shaft 2 perform a major role oftransmitting the torque.

For example, in a case where the torque is inputted from the male shaft1, the pre-load of the plate spring 9 being still applied at an initialstage, no backlash is caused, and the plate spring 9 generates reactionagainst the torque, thereby transmitting the torque. At this moment, thetotal torque transmitting is conducted in a state where a load of thetorque transmitting among the male shaft 1, the plate spring 9, thespherical members 7 and the female shaft 2 is equilibrated with a loadof the torque transmitting among the male shaft 1, the cylindricalmembers 8 and the female shaft 2.

As the torque further increases, the cylindrical member 8 receivesstronger reaction than the spherical member 7, since a clearance betweenthe male shaft 1 and the female shaft 2 in the rotation directionthrough the cylindrical member 8 is set smaller than a clearance betweenthe male shaft 1, the plate spring 9, the spherical member 7 and thefemale shaft 2 through the spherical member 7, with the result thatmainly the cylindrical member 8 transmits the torque to the female shaft2. It is therefore feasible to surely prevent the backlash in therotating direction between the male shaft and the female shaft 2 and totransfer the torque in the state of exhibiting the high rigidity.

Note that the spherical members 7, it is preferable, be rigid balls.Further, it is preferable that the rigid cylindrical members 8 be aneedle rollers.

There are variety of effects in which the cylindrical member (which willhereinafter be called the needle roller) 8 receives the load through aline-contact and can therefore restrain a contact pressure lower thanthe ball receiving the load through a point-contact, and so on.Accordingly, the following items are superior to a case where the ballrolling structure is adopted for all the lines.

-   -   A damping capacity effect at the slide portion is larger than in        the ball rolling structure. Hence, a vibration absorbing        performance is high.    -   If the same torque is transmitted, the needle roller can        restrain the contact pressure lower than the ball, whereby a        length in the axial direction can be decreased and a space can        be effectively utilized.    -   If the same torque is transmitted, the needle roller can        restrain the contact pressure lower than the ball, and hence        there is no necessity for an additional process for hardening        the surface of the axial groove of the female shaft by a thermal        treatment, etc.    -   The number of parts can be decreased.    -   An assembling characteristic can be improved.    -   An assembly cost can be restrained.

Thus, the needle roller 8 performs the key role of transferring thetorque between the male shaft 1 and the female shaft 2, and is broughtinto a slide-contact with the inner peripheral surface of the femaleshaft 2. The use of the needle roller has the following excellent pointsas compared with the conventional spline-fitting.

-   -   The needle roller is a product of mass-production and is        therefore extremely low of cost.    -   The needle roller is polished after the thermal treatment and is        therefore high of surface hardness and excellent of        anti-abrasion characteristic.    -   The needle roller is polished and is therefore fine of surface        roughness and low of friction coefficient when sliding, whereby        the slide load can be restrained low.    -   A length and a layout of the needle roller can be changed        corresponding to conditions for use, and hence there can be        given a flexibility to a variety of applications without        changing a design concept.    -   There might be a case in which the friction coefficient must be        decreased depending on the conditions for use, in this case the        slide characteristic thereof can be changed simply by effecting        a surface treatment on only the needle roller. Hence, there can        be given the flexibility to the variety of applications without        changing the design concept.    -   As the needle rollers can be manufactured at a low cost in a way        that differentiates their major diameters on a several-micron        basis, a clearance between the male shaft, the needle rollers        and the female shaft can be restrained to the minimum by        selecting the diameters of the needle rollers. Hence, an        improvement of the rigidity of the shaft in a torsional        direction can be facilitated.

On the other hand, the point that the spherical members (which willhereinafter be called balls) 7 are partially adopted, has the followingexcellent items as compared with the all-line-needle-roller andall-line-slidable structure.

-   -   The ball is low of the frictional resistance, and hence the        slide load can be restrained low.    -   The use of the ball can increase the pre-load, whereby the        prevention of the backlash over a long period of time and the        high rigidity can be simultaneously acquired.

FIG. 5 is the graph showing the relationship between the stroke of andthe slide load of the telescopic shaft for the vehicle steering in thefirst embodiment. FIG. 5 shows a comparison with a relationship betweenthe stroke of and the slide load of the telescopic shaft for the vehiclesteering that utilizes the ball rolling structure. It can be understoodfrom this comparison that the telescopic shaft for the vehicle steeringin the first embodiment is capable of restraining fluctuations in theslide load and exhibits a smooth slide characteristic.

Further, according to the first embodiment, as shown in FIG. 5, what canbe given as an extremely advantageous point is that the fluctuations inthe slide load are small over the entire torque area. Even in anystructures disclosed in, for example, German Patent ApplicationLaid-Open Publication DE3730393A1, a high pre-load must be given whentrying to eliminate the backlash in the peripheral direction and obtaina high rigidity in the peripheral direction, with the result that theslide load fluctuates at a ball rolling cycle. There is adisadvantageous point in which this produces an unpreferable feeling ofsteering as the shaft for the steering. Unlike the above-mentioned,according to the first embodiment, the needle rollers 8 exhibiting theextremely good slide characteristic are employed compositely with theballs 7, thereby making it possible to restrain the torque fluctuationsdue to the rolling of the balls 7 while restraining the rise in theslide load.

Further, when scheming to ensure the high rigidity in the radialdirection (the direction perpendicular to the axis) with theconstruction disclosed in German Patent Application Laid-OpenPublication DE3730393A1, a length to which the balls are interposed mustbe taken long, and this is limited in space and disadvantageous.Besides, there is such a disadvantageous point that in the case of theconstruction disclosed in this Publication, the male shaft is easy tofall down in the radiation direction about the balls interposed, andthis characteristic causes the unpreferable feeling of steering as theshaft for the steering. According to the first embodiment, the needlerollers 8 are interposed extending over the entire area of the rangewhere the balls 7 make reciprocating motions, and hence the rigidity inthe radial direction can be ensured at a high level.

Second Embodiment

FIG. 6 is a cross sectional view of the telescopic shaft for the vehiclesteering in a second embodiment of the present invention.

A different point of the second embodiment from the first embodiment isthat the first torque transmitting member involves the use of the rigidspherical members 7 in the first embodiment, and by contrast, accordingto the second embodiment, cylindrical members 14 as the first torquetransmitting member are so interposed as to be rollable.

In the second embodiment, the female shaft 2 is provided with an axialgroove 13 of which a bottom surface is formed flat, a plurality ofcylindrical members 14 of which axial direction is set orthogonal to thedirection in which the male shaft 1 and the female shaft 2 extend, and aholder 15 holds these cylindrical members 14. Other configurations, etc.are the same as those in the first embodiment discussed above.

The second embodiment also acquires the same features as those in thefirst embodiment and is effective in, as a matter of course, preventingthe backlash and in the case of aiming at further improving thetorsional rigidity and the durability. The spherical member 7 receivesthe load through the point-contact, and by contrast the cylindricalmember 14 receives the load through the line-contact (precisely, sinceneither the spherical member nor the cylindrical member is a perfectrigid member, the spherical member comes to have a circular or ellipticcontact surface, and the cylindrical member comes to have an elliptic orelongated contact surface). Namely, the cylindrical member 14 canreceive a higher load than by the spherical member 7 in the firstembodiment. Hence, an effect is that the pre-load applied onto thecylindrical member 14 can be increased, and essentially thetorsion-directional rigidity of the whole telescopic shaft can be moreimproved than in the first embodiment. It is preferable that thecylindrical member 14 be the needle roller.

Third Embodiment

FIG. 7 is an exploded perspective view of the telescopic shaft for thevehicle steering in a third embodiment of the present invention. FIG. 8is a perspective view of the holder shown in FIG. 7.

In the first embodiment (FIGS. 3 and 4) described above, the holder 12disposed between the male shaft 1 and the female shaft 2 has a pluralityof through-holes extending in the axial direction, and holds, e.g., thespherical members 7 as the first torque transmitting members. When themale shaft 1 and the female shaft 2 make the relative movements, theholder 12 also moves corresponding thereto.

The plurality of spherical members 7 are, however, received respectivelyin the plurality of through-holes, and hence there might be apossibility in which a speed difference occurs, and the slide resistanceis not stabilized.

Such being the case, according to the third embodiment, for the purposeof stabilizing the slide resistance, as shown in FIGS. 7 and 8, theholder 12 is formed with one elongate hole 12 a for receiving theplurality of spherical members on the whole. This is because if theholder 12 is provided with a pillar or partition in a limited space, thenumber of the spherical members 7 to be used decreases, and, if theholder 12 is not employed, the spherical members 7 are, though a largernumber of spherical members 7 can be received, to be scattered.

According to the third embodiment, the holder 12 becomes capable ofallowing the speed difference between the spherical members 7 owing tothe single elongate hole 12 a extending in the axial direction, and cantherefore stabilize the slide resistance. Further, the elimination ofthe pillar or partition from the holder 12 permits the number of thespherical members to increase so much for this elimination, andtherefore the contact pressure for every spherical member 7 can bereduced.

Fourth Embodiment

FIG. 9 is a cross sectional view of the telescopic shaft for the vehiclesteering in the first embodiment of the present invention. FIG. 10 is across sectional view of the telescopic shaft for the vehicle steering ina fourth embodiment of the present invention. FIG. 11 is a perspectiveview of the holder shown in FIG. 10.

In the first embodiment (FIGS. 3 and 4) described above, the holder 12disposed between the male shaft 1 and the female shaft 2 has theplurality of through-holes, and holds the spherical members 7. Theholder 12, when the male shaft 1 and the female shaft 2 make therelative movements, also moves corresponding thereto, and this movementin the axial direction is regulated by the stopper ring 11 of the maleshaft 1.

As shown in FIGS. 3, 4 and 9, however, the holder 12 has its end surfacethat is just a simple cut surface, so that there would be a fear thatthis end surface, when moving, does not abut on the stopper ring 11, andthe movement in the axial direction can not be regulated by the stopperring 11.

Such being the case, according to the fourth embodiment, for purpose ofmaking the holder 12 surely abut on the stopper ring 11, as shown inFIGS. 10 and 11, end portions of the holder 12 are respectively providedintegrally with tongue pieces 12 b. Note that the tongue pieces 12 b arenot limited to the configuration illustrated therein.

Thus, the holder 12 is provided integrally with the tongue pieces 12 bspreading large at the end portions thereof. Accordingly, when theholder 12 moves, the tongue pieces 12 b of the end surface thereofsurely abuts on the stopper ring 11, whereby the movement in the axialdirection can be surely regulated by the stopper ring 11 and the holder12 can be prevented from being damaged.

Fifth Embodiment First Example of Fifth Embodiment

FIG. 12 is a vertical sectional view of the telescopic shaft for thevehicle steering with a Cardan joint in a first example of a fifthembodiment of the present invention. FIGS. 13A through 13E are viewseach showing an example of the female shaft in the first example. FIG.14 is a view showing the female shaft in the first example. FIGS. 15Athrough 15E are views each showing an example of the male shaft in thefirst example.

As shown in FIG. 12, according to the first example, as an intermediateshaft for the steering, the male shaft 1 is connected to a yoke 21 of aCardan joint 20 on the side of the steering wheel, while the femaleshaft 2 is connected to a yoke 23 of a Cardan joint 22 on the side of asteering gear. Note that a stopper plate 11 a is used as a substitutefor the stopper ring 11. Other configurations and operations are thesame as those in the embodiments discussed above.

The attachment on the side of the steering wheel and the attachment onthe side of the steering gear may be reversed.

Next, FIGS. 13A through 13E and 14 show the examples of the female shaft2 serving as the shaft for the steering.

FIGS. 13A and 13B show the example of a sub-assembly state of the femaleshaft 2 and the yoke 23, wherein the yoke 23 is fitted into an insidediametrical portion of the female shaft 2, thus assembling them bywelding. The female shaft 2 is constructed of a large-diametercylindrical portion to which the yoke 23 is fitted and of asmall-diameter cylindrical portion having axial groves 5, 6 formed inits inner surface.

FIG. 13C shows another example of the sub-assembly state, wherein thefemale shaft 2 and the yoke 23 are fitted to each other, thus assemblingthem by welding. The female shaft 2 is formed with the axial grooves 5,6 extending over its entire length.

FIG. 13D shows still another example of the sub-assembly state, whereina serration portion formed in the side end portion of the female shaft 2is fitted to the yoke 23 and thereafter joined thereto by caulking aside endmost portion of the female shaft 2.

FIG. 13E shows yet another example equivalent to the sub-assembly,wherein the female shaft 2 and the yoke 23 are integrally molded bycold-molding, etc.

FIG. 14 shows a further example equivalent to the sub-assembly, whereinthe female shaft 2 is constructed integrally with a shaft member 24having, at its end portion, a serration for fitting a bolt fasteningtype yoke (unillustrated).

Next, FIGS. 15A through 15E show examples of the male shaft 1 as theintermediate shaft for the steering.

FIG. 15A shows the example of a sub-assembly state of the male shaft 1and the yoke 21, wherein the male shaft 1 is fitted into the yoke 21 andthereafter subjected to a welding work. The male shaft 1 has a steppedportion 10 a to which the stopper plate 11 a is attached.

FIG. 15B shows the example of the sub-assembly state of the male shaft 1and the yoke 21, wherein the male shaft 1 is fitted into the yoke 21 andthereafter subjected to the welding work. The male shaft 1 is formedwith the axial grooves 3, 4 extending over the entire length.

FIG. 15C shows another example equivalent to the sub-assembly, whereinthe male shaft 1 and the yoke 21 are integrally molded by thecold-molding, etc.

FIG. 15D shows an example of the sub-assembly state of the male shaft 1and the yoke 21, wherein a serration portion formed in the end portionof the male shaft 1 is fitted into the yoke 21 and thereafter joined tothe yoke 21 by caulking an endmost portion of the male shaft 1.

FIG. 15E shows an example of the sub-assembly state of the male shaft 1and the yoke 21, wherein the end portion of the male shaft 1 is fittedinto the yoke 21 and thereafter joined to the yoke 21 by caulking theendmost portion of the male shaft 1. The male shaft 1 is formed with theaxial grooves 3, 4 extending over its entire length.

Second Example of Fifth Embodiment

FIG. 16 is a vertical sectional view of the telescopic shaft for thevehicle steering in a second example of the fifth embodiment of thepresent invention. FIG. 17 is a vertical sectional view of the femaleshaft illustrated in FIG. 16. Note that FIGS. 15A through 15E are viewseach showing an example of the male shaft in the second example.

As shown in FIGS. 16 and 17, in the second embodiment, the female shaft2 as the main shaft for the steering is constructed integrally with theshaft member 25. This shaft member 25 has such a contrivance that thesteering wheel (unillustrated) is attached to its end portion. Thetelescopic shaft in the second embodiment is utilized as a steeringshaft having a telescopic function.

Next, FIGS. 15A through 15E show the examples of the male shaft 1 as themain shaft for the steering.

FIG. 15A shows the example of a sub-assembly state of the male shaft 1and the yoke 21, wherein the male shaft 1 is fitted into the yoke 21 andthereafter subjected to the welding work. The male shaft 1 has thestepped portion 10 a to which the stopper plate 11 a is attached.

FIG. 15B shows the example of the sub-assembly state of the male shaft 1and the yoke 21, wherein the male shaft 1 is fitted into the yoke 21 andthereafter subjected to the welding work. The male shaft 1 is formedwith the axial grooves 3, 4 extending over the entire length.

FIG. 15C shows another example equivalent to the sub-assembly, whereinthe male shaft 1 and the yoke 21 are integrally molded by thecold-molding, etc.

FIG. 15D shows an example of the sub-assembly state of the male shaft 1and the yoke 21, wherein the serration portion formed in the end portionof the male shaft 1 is fitted into the yoke 21 and thereafter joined tothe yoke 21 by caulking the endmost portion of the male shaft 1.

FIG. 15E shows the example of the sub-assembly state of the male shaft 1and the yoke 21, wherein the end portion of the male shaft 1 is fittedinto the yoke 21 and thereafter joined to the yoke 21 by caulking theendmost portion of the male shaft 1. The male shaft 1 is formed with theaxial grooves 3, 4 extending over its entire length.

Sixth Embodiment

FIG. 18 shows a cross sectional view of a principal portion of thetelescopic shaft for the vehicle steering by way of one example of theprior art. FIG. 19 is a cross sectional view of a principal portion ofthe telescopic shaft for the vehicle steering in a sixth embodiment ofthe present invention. Pairs of axial grooves 3, 4 and 5, 6 on which theball 7 and the needle roller 8 abut, are formed respectively in apredetermined curved-surface shape (e.g., a Gothic arched shape) as agroove configuration. This is also disclosed in, for example, JapanesePatent Application Laid-Open Publication No. 2001-50293.

As shown in FIG. 18, in a case where the groove configuration of theaxial grooves 3 through 6 is formed in the predetermined curved-surfaceshape (G, Gothic Arched shape), the ball 7 and the needle roller 8 abutthereon at contact points (C), and what will be given as below can besaid with respect to an initial contact angle, a torsion rigidity and acontact pressure (Pmax).

As for the initial contact angle, if a (±) torque is loaded, the balls 7and the needle roller 8 move along on the axial grooves 3 through 6taking the curved-surface configuration (G, Gothic arch) in a way thatchanges the contact angle (point). At this time, if the torque is loadedin forward→reversed directions, a friction affects the ball 7 and theneedle roller 8 to stay there. As a result, a hysteresis occurs in thetorsion rigidity. Due to a scatter in tolerance, as the contact point(C) of the ball 7 or the needle roller 8 gains a nearer vicinity to thebottom of the groove, the contact angle becomes shallower and thehysteresis becomes larger. Further, a contact angle in a nominal designposition is hard to obtain.

As for the torsion rigidity, the rigidity is low in a low torque area,however, as the torque increases, the contact point changes and thecontact angle becomes higher. Hence, a high rigidity is acquired in ahigh torque area.

As for the contact pressure (Pmax), in low-high torque states, a contactellipse is formed, and hence a rise in contact surface pressure ofespecially the ball 7 can be restrained.

Thus, in the case where the groove configuration of the axial grooves 3through 6 is formed in the curved-surface shape (G, Gothic archedshape), the torsion rigidity and the contact pressure (Pmax) areexcellent in the high torque area.

When assembling, however, as for the initial contact angle, it mightoccur that the ball 7, etc. does not always abut on the same positionwithin the axial groove 3, etc. due to a configuration error (tolerance)gap Min-Max when the ball 7, etc. is made to abut on the axial groove 3,etc. formed in the curved-surface shape, and the initial contact anglecan not be necessarily ensured.

Under such a circumstance, there is a demand for surely ensuring theinitial contact angle at the time of assembly (torque 0) in a way thatmakes use of the curved-surface shape (G. Gothic arched shape)exhibiting the excellent torsion rigidity and contact pressure (Pmax) inthe high torque area.

According to the sixth embodiment, as shown in FIG. 19, shallow areas ofthe axial grooves 3 through 6 are formed in the curved-surface shape (G,Gothic arched shape), while deep areas thereof are formed in a flatshape (F), wherein, e.g., the spherical member 7 as the first torquetransmitting member and, e.g., the cylindrical member 8 as the secondtorque transfer member abut on the groove in the vicinity of a boundarypoint between the curved area and the flat area thereof.

Thus, the area deeper than a contact point (C) is formed in the flatshape (F), and therefore, when assembling, the spherical member 7 andthe cylindrical member 8 are not affected by the configuration error(tolerance) gap Min-Max, whereby a desired contact angle or a contactangle more than desired can be surely ensured.

Thus, what will be given as below can be said in a case where thecurved-surface shape (G, Gothic arched shape) is combined with the flatshape (F).

Concerning the initial contact angle, at the time of assembly, in casethe spherical member 7 and the cylindrical member 8 abut on the flatarea (F), it is easy to obtain the initial (design) contact anglewithout being affected by a scatter in tolerance in the radialdirection.

Concerning the torsion rigidity, in the low torque area, since thespherical member 7 and the cylindrical member 8 abut on the flat shape(F), the initial contact angle as the design value manifests isobtained, and hence the high torsion rigidity is acquired.

On the other hand, in the area where the groove configuration takes theflat shape (F), if the torque becomes high, an elastic deformationoccurs, and a torsion quantity increases. Hence, in the high torquearea, the rigidity becomes lower than in the Gothic arched shape.

According to the sixth embodiment, however, the curved-surface shape (G,Gothic arched shape) is combined with the flat shape (F). Therefore, thespherical member 7 and the cylindrical member 8 abut on thecurved-surface shape (G, Gothic arched shape) exhibiting the excellenttorsion rigidity, wherein as the torque rises, the contact point changesand the contact angle becomes high. Hence, even in the high torque area,the high rigidity is obtained.

Concerning the contact pressure (Pmax), in the area where the grooveconfiguration takes the flat shape (F), the contact pressure of the ballbecomes higher as the torque rises.

According to the sixth embodiment, however, when the torque is applied,the contact points of the spherical member 7 and the cylindrical member8 gradually move onto the curved-surface shape (G, Gothic arched shape),and therefore the rise in the contact pressure can be restrained.

From the above-mentioned, in the sixth embodiment, the curved-surfaceshape (G, Gothic arched shape) is combined with the flat shape (F), sothat in the low torque area, the spherical member 7 and the cylindricalmember 8 abut on the flat shape (F), the initial contact angle as thedesign value manifests is obtained, and the high torsion rigidity isacquired; and on the other hand, in the high torque area, the sphericalmember 7 and the cylindrical member 8 abut on the curved-surface shape(G, Gothic arched shape), the high rigidity is obtained, and, as for thecontact pressure (Pmax), the increase in the contact pressure can berestrained.

Seventh Embodiment

FIGS. 20A and 20B are respectively vertical sectional views of thetelescopic shaft for the vehicle steering in a seventh embodiment of thepresent invention, showing a collapsible state when a secondarycollision of the vehicle happens. FIGS. 21A and 21B are verticalsectional views of the telescopic shaft for the vehicle steeringillustrated in FIG. 20, showing the collapsible state when the secondarycollision of the vehicle happens. FIGS. 22A through 22D are graphs eachshowing a relationship between the stroke and the slide load of thetelescopic shaft for the vehicle steering shown in FIGS. 20 and 21.

As a technical background of the seventh embodiment, the telescopicshaft for the vehicle steering is slidable (telescopic) in the axialdirection with a comparatively low and stable slide load (for instance,50 N or under) for a telescopic adjustment.

On the other hand, when the secondary collision of the vehicle happens,an impact energy of the secondary collision that is exerted towards thefront from the rear of the vehicle, is absorbed by generating a highslide load with an impact absorption mechanism provided in the steeringcolumn.

The impact absorption by only the column-sided impact absorptionmechanism brings about upsizing this impact absorption mechanism, and soforth. Therefore, in order to attain downsizing and decrease a weight ofthis column-sided impact absorption mechanism, there is a demand forsupplementing the column-sided impact absorption mechanism by having arole of absorbing the impact energy performed on the part of thesteering shaft also.

Under such a circumstance, according to the seventh embodiment, as shownin FIGS. 20 and 21, or as explained in the embodiments discussed above,there are interposed between the male shaft 1 and the female shaft 2,for example, the spherical members 7 as the first torque transmittingmembers biased by, e.g., the plate spring 9 as the elastic member andthe two pieces of, e.g., cylindrical members 8 as the second torquetransmitting members. With this arrangement, at a normal time, thetelescopic function and a displacement absorbing function of the carbody are exhibited with a low slide load. On the other hand, when thesecondary collision happens, the impact energy generated upon thesecondary collision is supplementally absorbed by generating a highslide load.

To be specific, when the secondary collision happens, the telescopicshaft of the steering shaft becomes collapsed, as seen in the sequencesuch as FIG. 20A→FIG. 20B→FIG. 21A→FIG. 21B, by the impact energyexerted from the rear towards the front of the vehicle.

Further, among the drawings in FIG. 22, FIG. 22A shows a state in FIG.20A, FIG. 22B shows a state in FIG. 20B, FIG. 22C shows a state in FIG.21A, and FIG. 22D shows a state in FIG. 21B.

The states shown in FIGS. 20A and 20B (corresponding to FIGS. 22A and22B) are states at the normal time, wherein the telescopic function andthe displacement absorbing function of the car body are exhibited withthe low slide load. There work both the rolling function of thespherical members 7 and the slide function of the cylindrical members 8.The slide load can be therefore restrained low.

Upon a start of the secondary collision, the telescopic shaft is strokedin its collapsing direction in the sequence such as FIG. 20A→FIG.20B→FIG. 21A. As shown in FIG. 21A, the spherical member 7 eventuallyabuts on a groove end portion (a cut-up portion) 26 of the male shaft 1and is thereby unable to roll any more. On this occasion, as illustratedin FIG. 22C, the high slide load occurs to initiate the supplementalabsorption of the impact energy.

As shown in FIG. 21B, when the male shaft 1 is intruded with a muchstronger load, the spherical members 7 start sliding between the femaleshaft 2 and the groove. With this operation, the telescopics and thecontractions of the telescopic shaft all turn out sliding motions,whereby, as shown in FIG. 22D, the high slide load can be acquired.Thus, when the secondary collision happens, the high slide load isgenerated, thereby enabling the supplemental absorption of the impactenergy caused by the secondary collision.

From the above-mentioned, the steering shaft is also made to perform therole of absorbing the impact energy when the secondary collisionhappens, thus supplementing the column-sided impact absorptionmechanism. Consequently, the downsizing and the reduction in weight ofthe column-sided impact absorption mechanism can be attained.

Moreover, the column-sided impact absorption mechanism is combined withthe impact absorption mechanism on the side of the steering shaft in theseventh embodiment, whereby an impact energy absorption timing can bestaggered. With this contrivance, at the initial stage of the collision,the energy absorption with the low load is not conducted by theshaft-sided absorption mechanism in the seventh embodiment, and, as thestroke progresses, the main absorption mechanism on the column side canabsorb the energy with the high load. The impact energy can be therebyabsorbed at a high efficiency within the limited space. Further, thereis a case where the system might work well depending on how to combinewith other restrictive supplement devices such as an airbag system, aseatbelt, etc. if the main energy absorption mechanism is notparticularly provided. This enables a further reduction in weight and afurther cost-down as well.

Note that the functions in the seventh embodiment are available for theintermediate shaft for the steering. The intermediate shaft can beseparately utilized as follows. In the low slide load range, theintermediate shaft is utilized for improving the assemblingcharacteristic to the vehicle or absorbing a relative displacement ofthe car body and for, in the high slide load range, absorbing the energycaused by the primary or secondary collision.

Eighth Embodiment

FIG. 23A is a vertical sectional view of the telescopic shaft for thevehicle steering in an eighth embodiment of the present invention. FIG.23B is a cross sectional view taken along the line b-b in FIG. 23A. FIG.24 is an exploded perspective view of the telescopic shaft for thevehicle steering in the eighth embodiment.

FIGS. 25 and 26 are graphs (characteristic line graphs obtained whenfixing one end of the male or female shaft and inputting the torque fromthe other end) each showing a relationship between a rotational angleand the torque of the telescopic shaft.

In the first embodiment discussed above, one pair of first torquetransmitting members 7 are disposed in one pair of axial grooves 3, 5,and the two pieces of second torque transmitting members are disposed inthe two pairs of axial grooves 4, 6 arranged at the equal interval of120 degrees in the peripheral direction with respect to the one pair ofaxial grooves 3, 5.

By contrast with this arrangement, according to the eighth embodiment,as shown in FIG. 23, the spherical members 7 as the first torquetransmitting members are disposed in three pairs of axial groovesarranged at the equal interval of 120 degrees in the peripheraldirection respectively through the plate springs 9 as the elasticmembers, thus structuring a first torque transmitting device. Thecylindrical members 8 as the second torque transmitting members aredisposed in three pairs of axial grooves 4, 6 disposed at a 60-degreeinterval in the peripheral direction between those three pairs of axialgrooves 3, 5, thus structuring a second torque transmitting device.

As a technical background for the eighth embodiment, a variety ofcharacteristics of the torsion rigidity are needed because of adifference in terms of its performance requested of every vehicle. Eachtime this requested characteristic was changed, a flexibility to therequested characteristic has hitherto been acquired by changing thestructure such as changing a diameter of the shaft or using the elasticmember.

In those cases, however, parts having various types of structures anddifferent elastic characteristics must be prepared, resulting inincreases in the number of parts and in the cost as well.

Such being the case, according to the eighth embodiment, as thecylindrical members 8 can be manufactured at a low cost in a way thatchanges the outside diameter thereof on the several-micron basis, aninterval between the male shaft, the cylindrical member 8 and the femaleshaft 2 can be arbitrarily set by properly selecting the diameter of thecylindrical member 8 or combining the diameters thereof. Thiscontrivance enables an easy adjustment of the characteristic of thetorsion rigidity of the telescopic shaft as will hereinafter be noted.

For instance, in the case of selecting the cylindrical member 8 having acomparatively large diameter, as shown in FIG. 23B, let ΔS be a gapbetween the male shaft 1 and the cylindrical member 8 or between thecylindrical member 8 and the female shaft 2, and a characteristic of ΔSappears to be ΔS1 as shown in the characteristic line graph of thetorsion rigidity in FIG. 25.

ΔS1 is a region where mainly the plate spring 9 is flexural and is aregion where a spring characteristic of the plate spring 9 appears. Notethat when the torque is loaded, the cylindrical member 8 abuts strong,and the torsion rigidity becomes by far higher than in the region of theplate spring 9.

As described above, in the case where the cylindrical member 8 havingthe comparatively large diameter is selected and ΔS is small, the regionin which the plate spring 9 works is small, and hence the torsionrigidity of the whole telescopic shaft increases. The springcharacteristic of the plate spring 9 has an influence on a feeling whensteering. Hence, in this case, the heterogeneous sounds and thevibrations do not cause problems, that is preferable to a case in whicha sharp feeling of the high rigidity is requested, and the low rigidityregion can be reduced to the greatest possible degree.

Inversely, in the case of selecting the cylindrical member 8 having acomparatively small diameter, ΔS increases, and, as indicated by ΔS2 inFIG. 26, the region in which the plate spring 9 works becomes large.Therefore, that is preferable to a case in which the heterogeneoussounds, the vibrations, etc. transferred from the road surface and fromthe power steering are made difficult to transmit to the handle as asteering feeling, and the low rigidity region where the plate spring 9works can be taken large.

From the above-mentioned, according to the eighth embodiment, thevariety of requests different depending on the characteristics of thevehicles as described above, can be met at a low cost without changingthe basic structure nor increasing the number of parts.

Ninth Embodiment

FIG. 27 is a cross sectional view of a principal portion of thetelescopic shaft for the vehicle steering in the conventional example asshown in FIG. 7 in DE3730393. FIG. 28 is a cross sectional view of aprincipal portion of the telescopic shaft for the vehicle steering in aninth embodiment of the present invention. FIG. 29 is a cross sectionalview of the principal portion of the telescopic shaft for the vehiclesteering illustrated in FIG. 28, showing an operation thereof. FIG. 30Ais a graph showing a relationship between the rotational angle and thetorque of the telescopic shaft in the conventional example. FIG. 30B isa graph showing a relationship between the rotational angle and thetorque of the telescopic shaft in the ninth embodiment.

As a technical background for the ninth embodiment, for example, in thecase of a pre-loading mechanism based on a configuration of the platespring in the conventional example shown in FIG. 27, the male shaft 1 isfixed, and, when a torque T is inputted from the female shaft 2, theball 7 is pushed strong against a contact point 30 br with a platespring 30. At this time, the plate spring 30 moves with a slightdeviation along on the male shaft 1 in a torque-applied direction. Then,the plate spring 30 acts to transfer the torque T while receiving strongreaction at a contact point 30 ar between the plate spring 30 and themale shaft 1. The plate spring 30 also abuts on another contact point 30a 1 with the male shaft 1 but is pushed strong against the contact point30 ar. When reversing the input torque T from this state, the ball 7begins to move in the opposite direction, however, the plate spring 30works, because of a friction with the male shaft 1, to stay in thatposition. With a further increase in torque, when the ball 7 moves, thecontact points 30 b 1 and 30 a 1 abut strong on each other. Note that ΔArepresents a quantity of movement of the ball 7 when loaded with thetorque T in FIGS. 27 and 29.

FIG. 30A shows how this phenomenon is graphed. The same torsion rigidityis not shown consistently when the torque is applied in the forwarddirection and when applied in the reversed direction, and a hysteresisquantity A occurs. If this hysteresis is large, a respondency tosteering declines.

Under such a circumstance, according to the ninth embodiment, as in thefirst embodiment, grooved portions 3 b, 3 b are formed extending inparallel with the groove 3 in the axial direction on both sides of theaxial groove 3 of the male shaft 1, and stepped portions 3 a, 3 a areformed between the axial groove 3 and the grooved portions 3 b, 3 b.Both side ends of the elastic member 9 taking substantially the M-shapein section extend respectively down to bottoms of the grooved portions 3b, 3 b, and its front side portions abut on the stepped portions 3 a, 3a so as to pinch these stepped portions 3 a, 3 a, respectively. Thus,concave portions 9 c, 9 c of the elastic member 9 engage with thestepped portions 3 a, 3 a provided on both sides of the axial groove 3of the male shaft 1, whereby the whole of the elastic member 9 is unableto move in the peripheral direction when transmitting the torque.

The elastic member 9 is thus formed and is therefore capable of, in thetelescopic shaft utilized for the steering shaft for the automobile,restraining over the long period of time the emission of theheterogeneous sounds and the decline in the steering feeling that arecaused by the backlash in the rotating direction. Besides, in the caseof applying the torque alternately clockwise and counterclockwise in therotating direction of the shaft, for the purpose of simply providing aless-hysteresis structure at a low cost, what is characteristic of theelastic member 9 provided with the pre-loading function is to have bothof a function of generating the pre-loads in the radial direction and inthe peripheral direction in a way that abuts at a certain fixed contactangle on, e.g., the spherical member 7 as the first torque transmittingmember, and a function of generating the pre-load only in the peripheraldirection.

It is desirable that the aforementioned elastic member 9 be the platespring 9. The method of utilizing the plate spring 9 as the pre-loadingmechanism as in the ninth embodiment has hitherto existed, however, thecharacteristic thereof was not at such a level as to satisfy itsperformance as the steering shaft. The reason for this lies in a problemabout the hysteresis occurred in the case of giving the torque clockwiseand counterclockwise in the rotating direction of the shaft.

In the ninth embodiment, as described above, the plate spring 9 ischaracterized by such a configuration as to have both of the function ofgenerating the pre-loads in the radial direction and in the rotatingdirection in a way that abuts at a certain fixed contact angle on thespherical member 7 and the function of generating the pre-load only inthe rotating direction, thereby providing the structure capable ofminimizing the hysteresis even in the case of reversing the torque asshown in FIGS. 28, 29 and 30B.

As illustrated in FIG. 28, when the torque is not given, the reaction(pre-load) acts on the plate spring 9 evenly on the right and left sideswith the ball 7 centered. There act reactions 9 er (9 el) and 9 dr (9dl) equilibrated with points 9 fr (9 fl) on which the spherical member 7abuts. At this time, as shown in FIG. 29, the male shaft 1 is fixed,and, when the torque T is inputted from the female shaft 2, thespherical member 7 is pushed strong against the contact point 9 fr withthe plate spring 9. At this moment, the spherical member 8 works totransmit the torque T while receiving the reaction strong at the contactpoint 9 er between the plate spring 9 and the male shaft 1.

Simultaneously, the reaction of the contact point 9 dl between the platespring 9 and the male shaft 1 increases. This reaction becomes a forceacting to move the spherical member 7 back to the center. When reversingthe input torque from this state, the plate spring 9 spontaneously worksto return to the original position by dint of the reaction generated atthe contact point 9 dl. A characteristic that the hysteresis isextremely small can be obtained even when reversing the torque with theaction of this centering function.

FIG. 30B is a graph showing this characteristic. Hystereses A and B havea relationship such as A>B, wherein it is possible to keep a state inwhich the responding performance when steering is extremely good.

As described above, the plate spring 9 is formed to have in combinationthe function of generating the pre-loads in the radial direction and inthe rotating direction in a way that abuts at a certain fixed contactangle on the spherical member 7 and the function of generating thepre-load only in the rotating direction, whereby the characteristic ofthe extremely good respondency when steering can be obtained.

Tenth Embodiment

FIG. 31A is a vertical sectional view of the telescopic shaft for thevehicle steering in a tenth embodiment of the present invention. FIG.31B is a cross sectional view taken along the line b-b in FIG. 31A. FIG.32 is a graph showing a relationship between a stroke and a slide loadin the tenth embodiment.

In the first embodiment discussed above, the one pair of first torquetransmitting members 7 are disposed in the one pair of axial grooves 3,5, and the two pieces of second torque transmitting members 8 aredisposed in the two pairs of axial grooves 4, 6 arranged at the equalinterval of 120 degrees in the peripheral direction with respect to theone pair of axial grooves 3, 5.

By contrast with this arrangement, according to the tenth embodiment,the spherical members 7 as the first torque transmitting members aredisposed in the three pairs of axial grooves 3, 5 arranged at the equalinterval of 120 degrees in the peripheral direction respectively throughthe plate springs 9 as the elastic members, thus structuring the firsttorque transmitting device. The cylindrical members 8 as the secondtorque transmitting members are disposed between those three pairs ofaxial grooves 3, 5, thus structuring the second torque transmittingdevice. Note that the second torque transmitting members 8, it ispreferable, be disposed respectively at the central portions in theperipheral direction between the three pairs of axial grooves 3, 5described above.

The tenth embodiment exhibits the following operations and effects.

A case where the torque is not applied: The plate springs 9 and thespherical members 7 are interposed between the male shaft 1 and thefemale shaft 2, and the pre-load is always applied, thereby maintainingthe no-backlash state. In this state, when extended or contracted in theaxial direction, there occur the rolling of the spherical members 7 andthe sliding of the cylindrical members 8. A this time, the slide loaddepends mainly on the rolling of the spherical members 7. Thecylindrical members 8 slide between the male shaft 1 and the femaleshaft 2 in a way that slightly is in contact with the male shaft 1 andthe female shaft 2.

A case where a small torque is applied: A contact pressure between themale shaft, the plate springs 9, the spherical members 7 and the femaleshaft 2 gradually rises as the torque is increasingly applied. With thisrise, the plate springs 9 start becoming flexural in the rotatingdirection. As the plate springs 9 become flexural in the rotatingdirection, a contact pressure between the male shaft 1, the cylindricalmembers 8 and the female shaft 2 gradually rises. When slid in thisstate, the contact pressure relative to the cylindrical members 8 hasbecome larger than in the state where the torque was not applied, andhence the slide load also increases slightly. Note that a contactpressure large enough to cause an indentation by the spherical members 7is produced neither on the plate spring 9 nor on the female shaft 2 inthis state. For example, under a condition that a torque equal to orsmaller than approximately 5 Nm is applied from a state where the torqueis zero, the load applied on the spherical members 7 is larger than theload on the cylindrical members 8, the characteristic of the torsionrigidity is influenced by spring constants of the plat springs 9.

A case where a large torque is applied: When the large torque isapplied, the torque is received mainly between the male shaft 1, thecylindrical members 8 and the female shaft 2, and therefore the contactpressure produced between the male shaft 1, the plate springs 9, thespherical members 7 and the female shaft 2 does not rise so much. Thecontact between the male shaft 1, the cylindrical members 8 and thefemale shaft 2 is the line-contacts (which are precisely defined aselongate ellipse contacts) and is therefore capable of enduring loadthat is by far larger than the point-contacts through the sphericalmembers 7. When slid in this state, the contact pressure through thecylindrical member 8 increases, so that the slide load becomes largerthan in the state where the small torque is applied. In case a torqueexceeding approximately 5 Nm is applied, the function of surelytransmitting the torque is preferential to the extending/contractingfunction. It may be said that a sufficient slide performance is providedif viewing in terms of the extending/contracting function and the torquetransmitting function with no backlash that are required of thetelescopic shaft for the vehicle steering.

According to the tenth embodiment, as shown in FIG. 32, a highlyadvantageous point to be given herein is that the fluctuation in slideload is small over the entire torque area. In any structures disclosedin, for instance, German Patent Application Laid-Open PublicationDE3730393A1, if schemed to obtain the high rigidity in the peripheraldirection with the peripheral backlash eliminated, the large pre-loadmust be applied, and it follows that the slide load fluctuates at theball rolling cycle. A disadvantageous point is that this fluctuationcauses an unpreferable feeling of steering as the shaft for the vehiclesteering. Unlike this, according to the tenth embodiment, thecylindrical members 8 exhibiting the highly good slide characteristicare employed compositely with the balls 7, thereby making it possible torestrain the torque fluctuations due to the rolling of the balls 7 whilerestraining the rise in the slide load.

Further, in the construction disclosed in German Patent ApplicationLaid-Open Publication DE3730393A1, if schemed to ensure the highrigidity in the radial direction (right-angled to the axis), a length towhich the balls are interposed must be taken long, and this isdisadvantageous because of a limit in space. Besides, in the case of theconstruction in this Publication, the male shaft is liable to fall downabout the balls interposed, and there is such a disadvantageous pointthat this characteristic produces the unpreferable feeling of steeringas the telescopic shaft for the vehicle steering. According to the tenthembodiment, since the cylindrical members 8 are interposed over theentire area of the range where the spherical members 8 make thereciprocating motions, the rigidity in the radial direction can beensured at a high level.

Superiority as the equi-disposed structure by every three trains: Trainsof the spherical members 7 plus the plate springs 9 are equally arrangedin three positions, whereby the male shaft 1 comes to a state of beingafloat from the female shaft 2. Accordingly, when the torque is applied,axial centers of the male shaft 1 and the female shaft 2 move topositions where the shafts 1 and 2 are balanced best with each other.For example, even if the male shaft 1, in the assembled state, becomes abit eccentric from the female shaft 2, the two shafts 1 and 2 work tobecome concentric as the torque is applied. Hence, when the torque isapplied, the stable torsion rigidity is obtained at all times. Moreover,the cylindrical members 8 are disposed between the trains of sphericalmembers 7, and hence the advantage is that the cylindrical members 8receive the load with a good balance on the occasion of receiving thetorque.

In a comparison between the tenth embodiment and the first embodiment,according to the tenth embodiment, the torque on which the pre-load bythe plate spring 9 acts falls within a range of 0 through approximately±5 Nm. By contrast, the first embodiment does not particularly discloseany numerical value of the torque which the pre-load acts on.

The tenth embodiment has a characteristic of being capable oftransmitting a much larger torque than in the first embodiment.According to the first embodiment, the torque that may not cause thespherical members 7 to generate a load of excessive contact pressureupon the action of the pre-load, is on the order of 2 Nm at the largest.If the torque is increased over 2 Nm, the excessive contact pressure isapplied. An excessive contact pressure is applied also to the sphericalmembers 7 with the result that the spherical members 7 might beindented, and the slide function is deteriorated. As compared with this,according to the tenth embodiment, the spherical members 7 and thecylindrical members 8 are equally arranged by three trains alternatelywith the well-balanced layout, and hence the torque transfer by thepre-load can be increased up to 5 Nm without bringing about any rise inslide load.

In the tenth embodiment, for the same reason, the cylindrical members 8abut strong before the plate springs 9 become flexural to the end,thereby making is feasible to restrain the contact pressure of thespherical members 7 and to set the maximum transmitting torque largerthan in the first embodiment.

It is preferable that the spherical members 7 be the balls. Further, itis preferable that the cylindrical members 8 be the needle rollers.

Eleventh Embodiment

FIG. 33A is a vertical sectional view of the telescopic shaft for thevehicle steering in an eleventh embodiment of the present invention.FIG. 33B is a cross sectional view taken along the line b-b in FIG. 33A.FIG. 34A is a perspective view of a holder shown in FIG. 33. FIGS. 34Band 34C are respectively perspective views of the holder in examples ofthe eleventh embodiment. FIGS. 35A, 35B and 35C are respectivelyperspective views of the holder in examples of the eleventh embodiment.

As a technical background for the eleventh embodiment, according to thetenth embodiment discussed above, when slid, all peripheral speeds ofthe spherical members 7 defined as the first torque transfer members arenot the same because of an influence of a difference of how much thepre-load is applied. Therefore, upon a start of sliding, relativepositions of the individual spherical members 7 change, and there occursuch a phenomenon that the spherical members 7 abut on each other andgaps between these member 7 are formed. In the state where no holder isprovided, this phenomenon occurs, and the slide resistance tends toincrease or fluctuate.

As in the tenth embodiment discussed above, in the case of having thecomposite function of the spherical members 7 and the cylindricalmembers, an average slide load itself can be set slightly larger than inthe case of only the rolling, however, since there is very few influenceon the slide load due to the phenomenon described above, there is notparticularly a problem in terms of the function even if the holder isnot provided.

For obtaining more stable slide load, however, it is preferable that thespherical members 7 be held by the holder.

Under such a circumstance, according to the eleventh embodiment, aholder 40 for holding the spherical members 7 in a rollable mannerwithout interfering with the cylindrical members 8, is disposed betweenthe male shaft 1 and the female shaft 2.

In the eleventh embodiment, as shown in FIGS. 33A and 33B, the firsttorque transmitting device is structured such that the spherical members7 as the first torque transmitting members are disposed in the threepairs of axial grooves 3, 5 equally disposed at the interval of 120degrees in the peripheral direction through the plate springs 9 as theelastic members. Then, in the second torque transfer device, thecylindrical members 8 as the second torque transmitting members aredisposed respectively in the axial grooves 4, 6 at the central portionsin the peripheral direction between those three pairs of axial grooves3, 5.

As illustrated in FIGS. 33A, 33B and 34A, the holder 40 for holding thespherical members 7 in the rollable manner without interfering with thecylindrical members 8, is disposed between the male shaft 1 and thefemale shaft 2.

This holder 40 taking a cylindrical shape has three pieces of elongateholes 41 for holding the spherical members 7 in the rollable manner, andalso has interference avoiding elongate holes 42, formed in positionscorresponding to the cylindrical members 8, for avoiding theinterference with the cylindrical members 8. The interference avoidingelongate holes 42 are formed by far longer in the axial direction thanthe elongate holes 41.

Further, in the example in FIG. 34B, the holder 40 takes the bottomedcylindrical shape, wherein a wall portion 43 is provided at one endthereof, and an interference avoiding open slits 44 opened at the otherend thereof are formed in addition to the three pieces of elongate holes41.

In the example in FIG. 34C, the holder 40 takes the bottomed cylindricalshape, wherein the wall portion 43 is provided at the other end thereof,and the interference avoiding open slits 44 opened at one end thereofare formed in addition to the three pieces of elongate holes 41.

In the example in FIG. 35A, the holder 40 taking the cylindrical shapehas three sets of pluralities of round holes 45 for holding thespherical members in the rollable manner, and also has interferenceavoiding elongate holes 42, formed in positions corresponding to thecylindrical members 8, for avoiding the interference with thecylindrical members 8.

In the example in FIG. 35B, the holder 40 takes the bottomed cylindricalshape provided with the wall portion 43 at one end, and has theinterference avoiding open slits 44 opened at the other end thereof inaddition to the three sets of pluralities of round holes 45.

In the example in FIG. 35C, the holder 40 takes the bottomed cylindricalshape provided with the wall portion 43 at the other end, and has theinterference avoiding open slits 44 opened at one end thereof inaddition to the three sets of pluralities of round holes 45.

From the above-mentioned, according to the eleventh embodiment, both ofthe spherical members 7 and the cylindrical members 8 exist on the sameaxial section, and nevertheless the spherical member 7 can be held,whereby the slide function can be improved (the slide load can bestabilized). As a result, a comfortable steering feeling can beobtained.

It is preferable that the spherical members 7 be the balls Further, itis preferable that the cylindrical members 8 be the needle rollers.

(Other Related Items)

The following items are, it can be said, applied to the whole of theembodiments of the present invention. When two pieces of cylindricalmembers 8 are disposed on the male shaft 1, the cylindrical members 8may be made fixed to the male shaft 1 to secure the cylindrical members8 to the male shaft 1 by caulking the surface of the male shaft 1 in thevicinity of the cylindrical members 8. The holder and the rollingmembers are held so as not to be separated from each other, whereby theassembly may also be facilitated. The male shaft is prevented from beingpulled out by caulking inwards the front side end of the female shaft,whereby a non-decomposable structure may thus be provided. Thecylindrical members 8, 14 and the spherical members 7, which haveundergone a thermal treatment and have been polished, may also be used.There may further be used the cylindrical member 8 of which the surfacehas been subjected to a resin layering process of a resin containingPTFE (polytetrafluoroethylene) or molybdenum disulfide. The male shaft 1manufactured by cold drawing from a solid or hollowed steel product, mayalso be available. The male shaft 1 manufactured by cold drawing from analuminum material, may further be available. The male shaft 1manufactured by cold forging from a solid steel product or an aluminummaterial, may still further be available. The female shaft 2manufactured by cold drawing molding from a hollowed steel product, mayalso be available. On the occasion of performing the cold forging of themale shaft, it is desirable that a metallic soap process (bonderizingprocess) be effected on the material. The female shaft may be made fromthe hollowed steel product as a material, wherein the steel product may,after undergoing the metallic soap process (bonderizing process), besubjected to a pipe-contracting or expanding work to a diameterrequired, and the grooves may be formed by press forming. The femaleshaft 2 may undergo nitriding. There may further be used the femaleshaft 2 of which the surface has been subjected to the resin layeringprocess of a resin containing PTFE (polytetrafluoroethylene) ormolybdenum disulfide.

Moreover, it is desirable that the ranges of the following numericalvalues be used in all of the embodiments of the present invention.

-   -   A diameter of the ball as the spherical member is on the order        of Φ3 mm through Φ6 mm in the application of being used for the        automobile.    -   A diameter of the needle roller as the cylindrical member is on        the order of Φ3 mm through Φ6 mm.    -   A P.C.D ratio of the ball diameter to the ball and the needle        roller is approximately 1:3.5 through 5.0.    -   As the torsion strength required of the automobile is generally        equal to or larger than 250 Nm, a diameter of the male shaft is        equal to or larger than 13 mm in the case of using a carbon        steel for a general mechanical structure.    -   In the state where the torque is not applied, a ball contact        pressure is equal to or smaller than 1500 MPa.    -   In a state where a torque on the order of 100 Nm is applied, the        ball contact pressure is equal to or smaller than 2000 MPa.    -   In the state where the torque on the order of 100 Nm is applied,        the needle roller contact pressure is equal to or smaller than        2000 MPa.    -   A ratio of a plate thickness of the plate spring to the ball        diameter is approximately 1:10 through 20.

It can be said that the present invention exhibits the followingadvantages as compared with the conventional products.

-   -   The cost is low.    -   The stable low slide load can be obtained.    -   No backlash is caused.    -   The anti-abrasion characteristic is excellent.    -   The heat resistance is excellent.    -   The weight can be reduced.    -   The mechanism is small.    -   There is the flexibility to any using conditions without        changing the design concept.

Note that each of Japanese Patent Application Laid-Open Publication No.2001-50293 and German Patent Application Laid-Open PublicationDE3730393A1 discloses the structure that the pre-load is applied by theelastic member, wherein the plurality of balls are interposed between inthe axial grooves formed in the male shaft and in the female shaft. Bycontract, the present invention, as described above, is by far moreexcellent than in [the case of taking the all-line ball rollingstructure] or [the case of taking the conventional spline-fitting].

Moreover, European Patent Application Laid-Open Publication EP1078843A1discloses a structure that the backlash is prevented by a regulator forpreventing the backlash in cooperation with the needle roller and theholder thereof, however, this is a pure sliding structure, and hence thepre-load can not be increased. It is therefore extremely difficult toprevent the backlash over a long period of time and to acquire the highrigidity.

In contrast with this, the present invention, as described above,partially adopts the rolling structure, has the different backlashpreventing means, and therefore exhibits the following excellent points.

-   -   The slide load can be restrained low because of the low        frictional resistance.    -   The pre-load can be increased, and it is possible to        simultaneously attain the prevention of the backlash over the        long period of time and the high rigidity.

As discussed above, according to the present invention, the first torquetransmitting device is constructed such that the spherical members asthe first torque transmitting members are interposed between in the pairof axial grooves formed in the outer peripheral surface of the maleshaft and in the inner peripheral surface of the female shaft throughthe elastic members for pre-loading; and the second torque transmittingdevice is constructed such that the cylindrical members as the secondtorque transmitting members are interposed respectively between in thetwo pairs of other axial grooves formed in the outer peripheral surfaceof the male shaft and in the inner peripheral surface of the femaleshaft.

When the torque is not transmitted, with the spherical members and thecylindrical members used, the elastic members applies the pre-load tothe spherical members and the cylindrical members against the femaleshaft to such an extent as to cause no backlash, thereby making itfeasible to surely prevent the backlash caused between the male shaftand the female shaft and enabling the male shaft and the female shaft toslide in the axial direction with the stable slide load without anybacklash.

When the torque is transmitted, the elastic member is structured torestrict the spherical member and the cylindrical member in theperipheral direction, whereby the torque can be transmitted in thehigh-rigidity state by surely preventing the rotation-directionalbacklash between the male shaft and the female shaft.

Note that the embodiments of the present invention have exemplified theballs as the spherical members, the needle rollers as the cylindricalmembers and the plate springs as the elastic members, but is not limitedto those members. Further, the present invention is not confined to theembodiments discussed above and can be modified in a variety of forms.

1. A telescopic shaft for vehicle steering, assembled into a steeringshaft of a vehicle and having a male shaft and a female shaft that areso fitted to each other to be able to transmit torque therebetween andmove in an axial direction relative to each other, comprising: a firsttorque transmitting device having: a first interposing portion with afirst axial groove and a second axial groove respectively provided in anouter peripheral surface of said male shaft and in an inner peripheralsurface of said female shaft, first torque transmitting membersincluding a plurality of spherical members disposed in the first andsecond axial grooves of said first interposing portion and rolling whensaid male shaft and said female shaft make relative movements in theaxial direction, and an elastic member disposed adjacent in a radialdirection to said first torque transmitting members in said firstinterposing portion, restricting said first torque transmitting memberswhen a torque is transmitted between said male shaft and said femaleshaft and applying a pre-load to said male shaft and said female shaftthrough said first torque transmitting members when torque is nottransmitted between said male shaft and said female shaft; and a secondtorque transmitting device having: a second interposing portion with athird axial groove and a fourth axial groove respectively provided inthe outer peripheral surface of said male shaft and in the innerperipheral surface of said female shaft, and a second torquetransmitting member including a cylindrical member disposed in saidsecond interposing portion such that the cylindrical member extendsparallel to both said male shaft and said female shaft, and sliding whensaid male shaft and said female shaft make the relative movements in theaxial direction, wherein the first and second torque transmittingdevices are arranged such that, in a first range of torque, torque istransmitted between said male shaft and said female shaft by the firsttorque transmitting members but not the second torque transmittingmember, and, in a second range of torque greater than said first range,the second torque transmitting member acts to transmit torque betweensaid male shaft and said female shaft.
 2. A telescopic shaft for vehiclesteering according to claim 1, wherein said first torque transmittingdevice and said second torque transmitting device are disposed inpositions different in a circumferential direction between said maleshaft and said female shaft.
 3. A telescopic shaft for vehicle steeringaccording to claim 1, comprising a plurality of first torquetransmitting devices and a plurality of second torque transmittingdevices, the third and fourth grooves of each second torque transmittingdevice being disposed, in a circumferential direction, between adjacentpairs of first torque transmitting devices.
 4. A telescopic shaft forvehicle steering according to claim 1, wherein said elastic member is aplate spring.
 5. A telescopic shaft for vehicle steering according toclaim 1, wherein each of the first through fourth axial grooves includesa shallow portion and a deep portion, the shallow portion of each grooveis formed in a curved-surface shape, the deep portion of each groove isformed in a flat shape, each of said first torque transmitting membersabuts on one of the first and second axial grooves in the vicinity of aboundary between the respective curved-surface portion and therespective flat portion, and, in said second range of torque, the secondtorque transmitting member abuts on each of the third and fourth axialgrooves in the vicinity of a boundary between the respectivecurved-surface portion and the respective flat portion.
 6. A telescopicshaft for vehicle steering according to claim 1, wherein said male shaftis provided with a groove end portion for generating a large slide loadby restricting said first torque transmitting members from rolling inthe axial directions so as to supplementally absorb an impact energywhen a collision occurs.
 7. A telescopic shaft for vehicle steeringaccording to claim 3, wherein each cylindrical member of said pluralityof second torque transmitting devices is disposed with a gap in therespective second interposing portion.
 8. A telescopic shaft for vehiclesteering according to claim 1, wherein said elastic member abuts on saidfirst torque transmitting members at a contact angle, generatespre-loads in the radial direction and in a circumferential directionwhen a torque is not inputted to said male shaft and said female shaft,and generates the pre-load in the circumferential direction when thetorque is inputted to said male shaft or said female shaft.
 9. Atelescopic shaft for vehicle steering according to claim 3, wherein saidfirst torque transmitting devices are arranged equally at an interval of120 degrees in the circumferential direction, and each second torquetransmitting devices is disposed between a pair of first torquetransmitting devices which are adjacent in the circumferentialdirection.
 10. A telescopic shaft for vehicle steering according toclaim 9, wherein each second torque transmitting devices is equallyspaced in the circumferential direction between the pair of adjacentfirst torque transmitting devices.
 11. A telescopic shaft for vehiclesteering according to claim 1, further comprising a first torquetransmitting member holder for holding said first torque transmittingmembers in a rollable manner.
 12. A telescopic shaft for vehiclesteering according to claim 11, wherein said holder has an elongate holeor a plurality of round holes extending in the axial direction, and saidfirst torque transmitting members are disposed in said elongate hole orrespectively in said plurality of round holes.
 13. A telescopic shaftfor vehicle steering according to claim 11, wherein said holder has acylindrical shape and has an elongate hole extending in the axialdirection or a plurality of round holes arranged in the axial direction,and said first torque transmitting members are disposed in said elongatehole or respectively in said plurality of round holes.
 14. A telescopicshaft for vehicle steering according to claim 13, wherein said holderhas an interference-avoiding elongate hole or an interference-avoidingopen slit opened at an end portion of said holder for avoidinginterference with said second torque transmitting device.
 15. Atelescopic shaft for vehicle steering according to claim 14, wherein atotal length of the interference-avoiding elongate hole or of theinterference-avoiding open slit is longer than a total length of saidelongate hole or a train of said plurality of round holes for holdingsaid first torque transmitting members.
 16. A telescopic shaft forvehicle steering according to claim 1, wherein in said second range oftorque, torque is transmitted between said male shaft and said femaleshaft by the first torque transmitting members and the second torquetransmitting member.
 17. A telescopic shaft for vehicle steeringaccording to claim 1, wherein the cylindrical member is disposed with agap in said second interposing portion.
 18. A telescopic shaft forvehicle steering according to claim 7, wherein each gap is arbitrarilyset by properly selecting a diameter for each second torque transmittingmember or by combining diameters of said male shaft, said female shaft,and each second torque transmitting member.